GJ 273 c
Astrophysical Synthesis & Habitability Characterization
GJ 273 c is a confirmed terrestrial exoplanet orbiting the star GJ 273, located approximately 19.3 light-years (5.92 parsecs) from the Solar System. First announced in 2017 by La Silla Observatory using the Radial Velocity detection technique (measuring periodic Doppler reflex motion in the host star's spectrum), this world measures 1.06 Earth radii and has a measured mass of 1.18 Earth masses. Combining its mass and radius yields a mean bulk density of 5.46 g/cm³ (a terrestrial silicate-iron composition comparable to Earth (5.51 g/cm³)), a surface gravity of 1.05 g⊕ (10.3 m/s²), and an escape velocity of 11.8 km/s.
In its orbital architecture around GJ 273, GJ 273 c completes one full revolution every 4.723 Earth days at a semi-major axis of 0.036467 AU (an ultra-close orbit less than one-seventh of Mercury's 0.387 AU distance from the Sun, where strong stellar tidal forces typically induce synchronous rotation). Its mean orbital velocity is approximately 84 km/s (compared to Earth's 29.8 km/s). Its moderate orbital eccentricity of e = 0.17 carries the world between 0.0303 AU at periapsis and 0.0427 AU at apoapsis, driving measurable seasonal insolation cycles.
⚠️ Thermal Regime (Irradiated / Hot Zone): At an equilibrium temperature of 462 K (+189°C / +372°F) and receiving 6.66 S⊕ (~9,064 W/m²), GJ 273 c orbits interior to the runaway greenhouse boundary where surface liquid water cannot persist.
The host star GJ 273 is classified as a low-mass red dwarf of spectral type M3.5 with an effective photospheric temperature of 3,382 K, a radius of 0.293 R☉, a mass of 0.29 M☉, an estimated bolometric luminosity of 0.01 L☉. Stellar evolution modeling indicates a metallicity of [Fe/H] = 0.09 dex (metal-rich relative to the Sun). From Earth, GJ 273 shines at apparent V-band magnitude 9.84 (accessible to binoculars and small amateur telescopes) in the Northern celestial hemisphere. The GJ 273 system is a multi-planet architecture hosting 2 confirmed worlds, with GJ 273 c sharing its stellar neighborhood alongside GJ 273 b.
Methodology: Computed using the Schulze-Makuch et al. (2011) weighted metric comparing physical interior (radius, estimated density) and surface thermal regime (escape velocity, equilibrium temperature).
Discovery Facility: La Silla Observatory · Catalogue Source: NASA Exoplanet Archive (IPAC / Caltech).
☀️ Host Star Telemetry
| Host Star Name | GJ 273 |
| Spectral Type | M3.5 |
| Effective Temp (Teff) | 3,382 K |
| Stellar Radius | 0.2930 R☉ |
| Stellar Mass | 0.2900 M☉ |
| Bolometric Luminosity | 0.01 L☉ |
| Metallicity [Fe/H] | 0.090 dex |
| Stellar Age | — |
| Apparent Magnitude | V: 9.840 |
| System Architecture | 1 Star, 2 Planets |
🪐 Orbital & Physical Dynamics
| Semi-Major Axis (a) | 0.036467 AU |
| Orbital Period | 4.723 days |
| Mean Orbital Velocity | 84 km/s |
| Orbital Eccentricity (e) | 0.17000 |
| Orbital Inclination (i) | — |
| Mean Bulk Density | 5.46 g/cm³ (11.8 km/s vesc) |
| Insolation Flux | 6.6600 S⊕ (~9,064 W/m²) |
| Habitable Zone Status | Exterior / Non-HZ |
| Celestial Distance | 19.300 LY (5.922 pc) |